1. Field of the Invention
The present invention relates to a VOD (Video on Demand) service, and more particularly to an apparatus and method for providing a high speed download service of multimedia contents capable of converting a format of a multimedia contents file used for a download service.
2. Background of the Related Art
A multimedia contents file for a VOD service may be created in an MP4 file format, for example, and constructed to effectively implement a streaming service. For example, FIG. 1 illustrates a structure of a general MP4 file format. As shown, the MP4 file is roughly divided into a ‘moov’ part corresponding to a header part and a ‘mdat’ part containing actual media information.
The ‘moov’ part includes a plurality of ‘trak()’ boxes holding meta information on each media according to a type of the media included in the multimedia contents file. That is, the trak boxes include a ‘trak(video)’ including meta information on video information, a ‘trak(audio)’ including meta information on audio information, and a ‘trak(hint)’ provided for a real time streaming service.
The multimedia contents file constructed with such a file format as shown in FIG. 1 is suitable for a streaming service. The VOD service provides the streaming service and a download service together based on the above-structured multimedia contents file.
In general, when creating a file suitable for the streaming service, functions making an internal structure of the file complicated are included to handle problems that may arise when the stream service is provided on a real time basis. A typical function is the construction of a multiple video trak by applying a temporal scalability. In more detail, FIG. 2 illustrates an example of a streaming service using a temporal scalability-based file format, in which the transmission of a base layer video and an enhancement layer video are controlled according to an available bandwidth of a network.
In other words, if an available bandwidth of the network is low, an RTP (Real Time Protocol) streaming server carries only the base layer video on an RTP packet, whereas if the available bandwidth of the network is higher than a prescribed value, the RTP streaming server transmits the enhancement layer video having a B (bi-directional)-frame as well as the base layer video so that a user can be provided with a video service with a high frame rate. In this instance, however, although the B-frame is advantageous in the aspect of the transmission error and scalability, it increases a transmission quantity.
Further, if the available bandwidth of the network is too low to transmit the base layer video, the RTP streaming server transmits only an I (intrinsic)-frame for service. However, in such a streaming service method, significant data is added to additionally store the enhancement layer video or the like, so that when the multimedia contents file is provided as a download service, the amount of data to be transmitted is significantly increased.
Further, because the number of packets required for transmission of the entire multimedia contents file is increased, the user's service fee is increased and a lot of time is required for the user to download the file for service.
Turning now to FIG. 3, which illustrates a format of the multimedia contents file including a multi bit-rate media. One multimedia contents file includes multi bit-rate coded video and audio data. The multimedia contents file as shown in FIG. 3 has a structure that can be serviced by selecting video and audio data suitable for the available bandwidth of the network such as the temporal scalability.
If the available bandwidth of the network is not less than 256 Kbps, a video V3 and an audio A3 are streaming-serviced, while if the available bandwidth is not more than 64 Kbps, quite low, a video V1 and an audio A1 are streaming-serviced.
However, even though the multimedia contents file having the structure including the multi bit-rate coded media is used for the download service, the number of packets required for transmission of the entire file is increased, which results in a higher service fee and increases a user's standby time for using the service.